Amplifier-mixer device

ABSTRACT

NL0200232ier-mixer device comprising: an amplifier structure having at least one amplifier input and at least one amplifier output, while at least one of the amplifier outputs is looped back via a feedback to at least one of the amplifier inputs. The amplifier structure comprises a mixer structure. The mixer structure comprises at least one switch having a switch input communicatively connected with the radio input, and a switch output communicatively connected with the mixer output, which switch input and switch output in a conducting state of the switch are electrically connected with each other and in a non-conducting state of the switch are electrically substantially not connected with each other and which switch in use is switched from the conducting state to the non-conducting state and vice versa with the local oscillator signal.

[0001] The invention relates to an amplifier-mixer device comprising: anamplifier structure having at least one amplifier input and at least oneamplifier output, while at least one amplifier output is looped back viaa feedback to at least one amplifier input, which amplifier structurecomprises a mixer structure, having at least one radio inputcommunicatively connected with the amplifier input, for receiving asignal of a radio frequency; at least one local input for receiving alocal oscillator signal; and at least one mixer output for providing asignal of a medium frequency.

[0002] Such an amplifier-mixer device is known from the Dutch-languagepublication: “A bipolar switching mixer with overall feedback”, W. Muys,graduate report 68360/1990-10, Delft University of Technology 1989.

[0003] In the known amplifier-mixer device, the amplifier structure isdesigned as a two-stage amplifier in which a Common Base (CB) bipolarjunction transistor (BJT), of which the collector and emitter form theamplifier output, is replaced by a mixer structure. The mixer structureis designed as a Gilbert Cell mixer and comprises two BJTs whoseemitters are connected to each other. Of each of the BJTs, the base isconnected to a separate local oscillator source. These local oscillatorsources are connected to each other through a side not connected to anyof the bases, and operate in opposite phase. The mutually connectedsides of the local oscillator sources in the amplifier, as it were,replace the base of the CB bipolar transistor. The collectors of theBJTs constitute the positive and the negative junction, respectively, ofthe medium frequency output.

[0004] A drawback of this known amplifier-mixer device is the energyconsumption. This is disadvantageous specifically in applications with alimited source power, such as mobile telephones, radios or otherwireless applications. Moreover, the known amplifier-mixer device iscomparatively complex.

[0005] It is an object of the invention to provide an amplifier-mixerdevice which obviates these drawbacks. To that end, the inventioncontemplates the provision of an amplifier-mixer device which has alower energy consumption and has comparatively few components. Accordingto the invention, an amplifier-mixer device as described above ischaracterized, according to the invention, in that the mixer structurecomprises: at least one switch having a switch input which iscommunicatively connected with the radio input and a switch output whichis communicatively connected with the mixer output, which switch inputand switch output in a conducting state of the switch are electricallyconnected with each other and in a non-conducting state of the switchare electrically substantially not connected with each other and whichswitch in use is switched from the conducting state to thenon-conducting state and vice versa with the local oscillator signal.

[0006] Such an amplifier-mixer device has a lower energy consumptionbecause virtually no bias current flows through the switches and theswitches use power virtually exclusively when being set from thenon-conducting state into the conducting state or vice versa. Moreover,in the device, for the operation of the mixer structure, in contrast tothe Gilbert Cell mixer structure in the known amplifier-mixer device, nobias current source for the mixer structure needs to be used.Consequently, the number of components in the circuit is reduced, sothat both the energy consumption and the complexity of theamplifier-mixer device decrease. Also, an amplifier-mixer according tothe invention is simpler to implement in a single integrated circuit,with, for instance, all transistors being designed as field effecttransistors (FETs) and the other components being exclusively of apassive type, such as resistors, coils and capacitors.

[0007] Specific embodiments of the invention are laid down in thedependent claims.

[0008] Further aspects, details and embodiments of the invention will bediscussed with reference to the figures shown in the drawings.

[0009]FIG. 1 shows a block diagram of a twoport device.

[0010]FIG. 2 shows a block diagram of a first example of an embodimentof an amplifier-mixer device according to the invention.

[0011]FIG. 3 shows a circuit diagram of a second example of anembodiment of an amplifier-mixer device according to the invention.

[0012] In the following description, use has been made of the concept ofa nullor. This concept will be explained below with reference to thetwoport shown in FIG. 1. The twoport shown in FIG. 1 has an input with apositive input contact i⁺ and a negative input contact i⁻. An output ofthe twoport is formed by a positive output contact u⁺ with a negativeoutput contact u⁻. The parameters A, B, C and D are defined by thefollowing equations: $\begin{matrix}{{1/A} = ( \frac{U_{U}}{U_{i}} )_{I_{u} = 0}} & {( {{voltage}\quad {gain}} );} \\{{1/B} = ( \frac{I_{U}}{U_{i}} )_{U_{u} = 0}} & {({transadmittance});} \\{{1/C} = ( \frac{U_{U}}{I_{i}} )_{I_{u} = 0}} & {({transimpedance});} \\{{1/D} = ( \frac{I_{U}}{I_{i}} )_{U_{u} = 0}} & {( {{current}\quad {gain}} ).}\end{matrix}$

[0013] Here, U_(i) is the voltage difference of the input signal betweenthe positive input contact i⁺ and the negative input contact i⁻. I_(i)is the current of the input signal in the direction of the arrowindicated with I_(i). U_(u) is the voltage difference of the outputsignal between the positive output contact u⁺ and the negative outputcontact u⁻. I_(u) is the current of the output signal in the directionof the arrow indicated with I_(u). The relation between the input andoutput signals can be described by the matrix equation below:$\begin{bmatrix}U_{i} \\I_{i}\end{bmatrix} = {\begin{bmatrix}A & B \\C & D\end{bmatrix}\begin{bmatrix}U_{u} \\I_{u}\end{bmatrix}}$

[0014] It can be derived that the input and output impedances equal:$\begin{matrix}{Z_{i} = \frac{{A\quad Z_{1}} + B}{{C\quad Z_{1}} + D}} \\{Z_{u} = \frac{{D\quad Z_{s}} + B}{{C\quad Z_{s}} + A}}\end{matrix}$

[0015] In these impedance equations, Z_(i) is the input impedance of thetwoport; Z_(u) is the output impedance of the twoport; Z_(l) is the loadimpedance and Z_(s) is the source impedance.

[0016] In the present application, a nullor is understood to mean: atwoport of the type shown in FIG. 1, with the parameters A, B, C and Dbeing substantially infinitely small or to be so considered in thespecific implementation.

[0017] In FIG. 2 an amplifier-mixer device VM is shown. Theamplifier-mixer device VM comprises an amplifier structure V. Theamplifier structure V has an amplifier input and an amplifier output.The amplifier input is formed by a positive input contact i⁺ and anegative input contact i⁻. To the amplifier input a radio-frequency(r.f.) signal can be presented. The r.f. signal can be presented to theamplifier input contacts i⁺, i⁻ as an electric current or a voltagedifference between the positive input contact i⁺ and the negative inputcontact i⁻. The amplifier structure proceeds to amplify the r.f. signaland outputs it to the amplifier output of the amplifier structure Vwhich is formed by a positive output contact u⁺ and a negative outputcontact u⁻.

[0018] The amplifier structure can be any kind of amplifier structure,for instance a differential amplifier, a power amplifier, atransadmittance amplifier or a transconductance amplifier.

[0019] The positive output contact u⁺ has been looped back via aresistor R3 to the negative input contact i⁻. It is also possible,instead or in addition, to loop the negative output contact back to thepositive input contact, optionally via a coupling impedance Z4, as isrepresented in FIG. 2 with dotted lines 1. It will be clear that thefeedback can be of any type and that the feedback can be direct orindirect, with one or more coupling elements.

[0020] The amplifier structure V comprises a mixer structure MX. Ther.f. signal that is presented to the amplifier input contacts i⁺,i⁻ ispassed, in the interior of the amplifier structure V, to a radio inputRF of the mixer structure MX, as is indicated with dotted lines 2,3. Inthe mixer, the r.f. signal is mixed with a local oscillator (l.o.)signal. This mixing results in a signal of medium or intermediatefrequency (i.f.), which is presented to a mixer output. In theamplifier-mixer device shown in FIG. 2, the mixer output is formed by apositive i.f. contact IF⁺ and a negative i.f. contact IF⁻.

[0021] The mixer structure MX comprises two switches S1 and S2. Theswitches S1, S2 each have a switch input Sin and a switch output Sout.The switch inputs Sin are communicatively connected with the radio inputof the mixer structure MX, so that the r.f. signal is passed to theswitches. In the figure, the switch S1 is in a conducting state in whichthe switch input Sin is conductively connected with the switch outputSout, while the switch S2 is in a non-conducting state in which theswitch input Sin has no conductive connection with the switch outputSout. In use, the switches are switched from one state to the otherstate and vice versa with a local oscillator signal by the LO signalthat is passed to the switches via a positive local contact LOp and anegative local contact LOn. As a result, the signal that is presented tothe switch inputs Sin is mixed with the local oscillator signal, whichresults in an i.f. signal. This signal can be tapped at the switchoutputs Sout and be further used via the mixer output contacts IF⁻ andIF⁺. It will be clear that the specific manner in which switching iscarried out depends on the type of switch used in the mixer structure.

[0022] By the use of a mixer structure with switches, the mixerstructure consumes power virtually exclusively if the switches are inthe conducting state. Moreover, such a mixer structure does not need anybias current, and no bias current source is needed. Also, such astructure has the properties of a nullor. This makes it relativelysimple to describe the amplifier characteristic and implement it in acircuit.

[0023] It will be clear that the Gilbert cell used in the knownamplifier-mixer device functions only if through the mixer transistors abias current flows from the collector to the emitter. This bias currentis a direct current and is obtained by a bias current source connectedto the emitters. If to the bases of the mixer transistors in the Gilbertcell the LO signal is presented and at the emitters the r.f. signal issuperposed on the bias current, then on the collector side the i.f.signal will be obtained in the form of a current superposed on the biascurrent. The use of a mixer structure according to the invention makesit possible to omit the bias current source because the r.f. signal ismixed by bringing the switches from the conducting state into thenon-conducting state and vice versa.

[0024] The switch outputs Sout of the switches S1 and S2 are coupled toeach other through resistors R1 and R2. The switches are switchedsubstantially in opposite phase with respect to each other, so that atthe mutually coupled contacts of the resistors R1 and R2 an r.f. signalis obtained which can be outputted to the amplifier output, in thefigure to the positive output u⁺. It will be clear that it is possibleto combine the signals in a different manner, for instance by means ofcoils, capacitors, additional amplifier stages or other more complexelectrical components.

[0025] In the second example of an embodiment of an amplifier-mixerdevice according to the invention shown in FIG. 3, the switches aredesigned as field effect transistors (FETs). In the amplifier-mixerdevice VM shown in FIG. 3, the amplifier structure V is a two-stageamplifier, in which a first stage is formed by a differential amplifierDV, and a second stage by the mixer structure MX.

[0026] The differential amplifier DV is formed by two n-type Metal OxideSilicon (MOS) FETs TV1 and TV2, whose sources are connected with eachother and a current source I. The drains of the transistors TV1 and TV2are connected through resistors R11 and R12, respectively, with a supplyvoltage VCC and form the output contacts of the first amplifier stage.The gates of the transistors form the input contacts i⁺,i⁻ of theamplifier-mixer device.

[0027] The drains of the transistors TV1 and TV2 are each connected to arespective pair of switches S1, S2, and S3, S4 of the mixer structureMX. The switches S1-S4 are N MOS-FETs, whose voltage across the gate isswitched with the local frequency. The voltage across the gate is thenset such that the FETs S1-S4 are operative in the triode range, so thatthe FETs function as switch. The switch inputs Sin are formed by thedrains of the FETs and the switch outputs Sout are formed by thesources. Of each respective transistor pair S1, S2, and S3, S4, thetransistors are switched in opposite phase with respect to each other,in that the gate of one transistor is connected to the negative localcontact LOn and the gate of the other transistor is connected to thepositive local contact LOp. Resistors R1, R3 and R5, R7, respectively,combine the i.f. signals of each pair similarly to the resistors R1 andR2 in FIG. 2, so that the mutually connected contacts of the resistorsR1, R3 and R5, R7 respectively form the negative output contact u⁻ andthe positive output contact u⁺ of the two-stage amplifier. At theseoutput contacts, the amplified r.f. signal is available. In theamplifier-mixer device VM shown in FIG. 3, the negative output contactu⁻ and the positive output contact u⁺, respectively, are coupled back tothe input contacts i⁺ and i⁻, respectively, via resistor R10 andcapacitor C1, and resistor R9 and capacitor C2. Capacitors C1 and C2 inthe feedback ensure that no bias current flows through the FETs S1-S4.

[0028] Due to the amplifier transistors TV1 and TV2 being switched inopposite phase (the r.f signal presented to the input contacts i⁺,i⁻ isbalanced), the i.f. signals of the FETs S1 and S4 have the same phase.The signal coming from FET S4 is switched with twice a 180 degree phasedifference with respect to the FET S1 signal: a first time with 180degrees phase difference by FET TV2 with respect to FET S1 and a secondtime with 180 degrees phase difference by the negative local inputcontact LOn with respect to the positive local input contact LOp. Thisresults in a total phase difference of 360 degrees, which is equivalentto a phase shift of 0 degrees. Similarly, the i.f. signals of the FETsS2 and S3 are equal in phase, having a phase difference of 180 degreeswith the i.f. signal of the FETs S1 and S4. Consequently, the i.f.signals of equal phase can be combined. This has been implemented in thedevice in FIG. 3 by the resistors R2, R8 and R4, R6, respectively. As aresult, a balanced i.f. signal is obtained at the mixer output.

[0029] Both mixer output contacts IF⁻, IF⁺ are grounded via a capacitorC3 and C4, respectively, so that undesired frequency components arefiltered from the i.f. signal.

[0030] The invention is not limited to the embodiments shown. After theforegoing, different variants will readily occur to those skilled in theart. It will be clear that the input contacts and output contacts may beconnected with each other in any manner. In particular, it will bereadily understood the contacts can be designed in the manners as knownfrom E. H. Nordholt, “The design of high performance negative feedbackamplifiers” and the manners known from the Dutch-language patentpublication 87 01026, incorporated into this application by reference.

[0031] It will also be obvious to design transistors in the amplifierdevice and/or the mixer structure in a complementary version, with, forinstance, the N-type FETs replaced with P-type FETs and vice versa.Also, it will be obvious to substitute transistors of a particular typeby a different type, for instance FET by BJT. It is likewise obvious toreplace the resistors shown with capacitances and inductances. Also, itwill be clear to those skilled in the art that the amplifier structureand/or the mixer structure can be designed in a different manner, forinstance by adding extra amplifier stages in the form of transistors oradding extra nullors. Additionally, it is not necessary to design theamplifiers as nullors.

[0032] The invention is not limited to an integrated circuit or aparticular topology. In particular, an amplifier-mixer device accordingto the invention can be designed as an assembly of discrete componentsor an at least partly integrated circuit of Complementary Metal OxideSilicon (CMOS), merged CMOS and bipolar (Bi-CMOS), Silicon Germanium(SiGe), Gallium Arsenide (GaAs) or similar structures.

[0033] Also, it will be obvious to realize the summation of RF and IFsignals not with resistors but with, for instance, active componentssuch as MOS or BJT devices.

1. An amplifier-mixer device comprising: an amplifier structure havingat least one amplifier input and at least one amplifier output, while atleast one amplifier output is coupled back via a feedback to at leastone amplifier input, which amplifier structure comprises a mixerstructure, having at least one radio input, communicatively connected tothe amplifier input, for receiving a signal having a radio frequency; atleast one local oscillator input for receiving a local oscillatorsignal; and at least one mixer output for providing a signal having amedium frequency, characterized in that the mixer structure comprises:at least one switch having a switch input communicatively connected withthe radio input and a switch output communicatively connected with themixer output, which switch input and switch output in a conducting stateof the switch are electrically connected with each other and in anon-conducting state of the switch are electrically substantially notconnected with each other and which switch in use is switched from theconducting state to the non-conducting state and vice versa with thelocal oscillator signal.
 2. An amplifier-mixer device according to claim1, wherein the mixer structure comprises at least two switches, which inuse are switched substantially in opposite phase with respect to eachother with the local oscillator signal, and of which switches the switchoutputs are connected with each other via at least one connectingcomponent, while an output contact of the connecting components that isnot connected to the switch outputs forms at least one of the amplifieroutputs.
 3. An amplifier-mixer device according to claim 2, wherein theamplifier structure comprises a differential amplifier, of which atleast one input is connected with the at least one amplifier input andin which the mixer structure comprises at least four switches, of whichat least four switches at least one first pair switched in oppositephase is connected with a positive output contact of the differentialamplifier and at least one second pair switched in opposite phase isconnected with a negative output contact of the differential amplifier.4. An amplifier-mixer device according to any one of the precedingclaims, wherein the amplifier structure comprises a first amplifier anda second amplifier and wherein an input of the first amplifier forms afirst input contact of the amplifier structure and an input of thesecond amplifier forms a second input contact of the amplifierstructure.
 5. An amplifier-mixer device according to claim 3, whereinthe first amplifier and the second amplifier are connected with eachother while balanced.
 6. An amplifier-mixer device according to claim 5,wherein an input of the first amplifier is connected by a first crosscoupling with an output of the second amplifier, and an input of thesecond amplifier is connected by a second cross coupling with an outputof the first amplifier.
 7. An amplifier mixer device according to claim5 or 6, wherein the first amplifier and the second amplifier are furtherconnected with each other through a parallel coupling, which connects aninput or an output of the first amplifier with a corresponding input oroutput of the second amplifier.
 8. An amplifier-mixer device accordingto any one of the preceding claims, wherein the couplings compriseexclusively passive electronic components.
 9. An amplifier-mixer deviceaccording to any one of the preceding claims, wherein the amplifierstructure is substantially designed as at least one nullor structure.10. An amplifier-mixer device according to any one of the precedingclaims, wherein at least one of the switches is a FET transistor, ofwhich the gate forms the local input and the source and the drain formthe switch input and the switch output, respectively.
 11. Anamplifier-mixer device according to any one of the preceding claims,wherein at least one of the switches is a FET transistor, of which thegate forms the local input and the drain and the source form the switchinput and the switch output, respectively.
 12. A method for amplifyingand mixing a signal, comprising: amplifying an input signal, comprising:receiving the input signal; amplifying the input signal to form anamplified signal; outputting the amplified signal as output signal;feeding back the output signal as input signal; said amplifying furthercomprising: receiving a signal of a radio frequency; receiving a localoscillator signal of local oscillator frequency; and mixing the signalof radio frequency with the local oscillator signal to form a signal ofmedium frequency and outputting the signal of medium frequency;characterized in that mixing comprises: switching with the localoscillator signal at least one switch from a conducting state of theswitch, wherein a switch input where the signal of radio frequency ispresented and a switch output where the signal of medium frequency isoutputted are electrically connected with each other, to anon-conducting state of the switch, wherein the switch input and theswitch output are electrically substantially not connected with eachother, and vice versa.